Monodisperse latexes

ABSTRACT

Methods for forming a latex are provided. In an embodiment, such a method comprises adding a monomer emulsion comprising water, a monomer, an acidic monomer, a multifunctional monomer, a first reactive surfactant, and a chain transfer agent, to a reactive surfactant solution comprising water, a second reactive surfactant, and an initiator, at a feed rate over a period of time so that monomers of the monomer emulsion undergo polymerization reactions to form resin particles in a latex, wherein the reactive surfactant solution does not comprise monomers other than the second reactive surfactant, the reactive surfactant solution does not comprise a resin seed, and the monomer emulsion does not comprise the resin seed. The latexes are also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 17/102,507, which was filed on Nov. 24, 2020, theentire contents of which are hereby incorporated by reference.

BACKGROUND

Latexes for aqueous inkjet ink compositions are often synthesizedthrough emulsion polymerization or microemulsion polymerization ofhydrophobic monomers in water. To render the resin particles of thelatex small and colloidally stable, large amounts of surfactants, suchas sodium dodecyl sulfonate (SDS) are often used. Excess surfactant inthe resulting latex causes problems in formulating the aqueous inkjetink compositions, such as foaming and reduction in surface tension. Theremoval of excess surfactant also adds cost, complexity, time, and leadsto colloidal instability. In addition, the size distribution of theresin particles of the resulting latex is generally broad. Even a smallnumber of large resin particles can induce particle sedimentation andnozzle clogging during printing of aqueous inkjet ink compositionsformed from the latex.

Aqueous inkjet ink compositions generally include water,water-dispersible pigments, hydrophilic solvents, and binding resins.The binding resins may be provided by certain latexes as noted above.Latexes are useful as they can form water-impenetrable films to protectcolorant in images printed from the aqueous inkjet ink compositions.However, the addition of latexes to aqueous inkjet ink compositionsimposes a level of complexity and tends to compromise printing behaviorsuch as jetting instability, jetting latency, and nozzle clogging. Useof latexes in aqueous inkjet ink compositions also reduces theshelf-life of the compositions.

SUMMARY

The present disclosure provides methods for forming monodisperselatexes. Embodiments of the methods are able to achieve resin particleshaving a small size and narrow size distribution (e.g., D_((z, ave))≤150nm, D_((v, 90))≤200 and PDI≤0.05). This is thought to contribute, atleast in part, to greatly improved stability and printing performance ofaqueous inkjet ink compositions formed from the latexes. Themonodisperse latexes and aqueous inkjet ink compositions are alsoencompassed by the present disclosure.

Methods for forming a latex are provided. In an embodiment, such amethod comprises adding a monomer emulsion comprising water, a monomer,an acidic monomer, a multifunctional monomer, a first reactivesurfactant, and a chain transfer agent, to a reactive surfactantsolution comprising water, a second reactive surfactant, and aninitiator, at a feed rate over a period of time so that monomers of themonomer emulsion undergo polymerization reactions to form resinparticles in a latex. The reactive surfactant solution does not comprisemonomers other than the second reactive surfactant, the reactivesurfactant solution does not comprise a resin seed, and the monomeremulsion does not comprise the resin seed.

Latexes are also provided. In embodiments, such a latex comprises resinparticles comprising a polymerization product comprising a monomer, anacidic monomer, a multifunctional monomer, and a reactive surfactant,the resin particles having a D_((z, ave)) of no greater than about 150nm, a D_((v, 90)) of less than about 200 nm, and a PDI of no greaterthan about 0.050.

Other principal features and advantages of the disclosure will becomeapparent to those skilled in the art upon review of the followingdrawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the disclosure will hereafter be describedwith reference to the accompanying drawings.

FIG. 1 shows the size distribution of resin particles of a monodisperselatex formed according to an illustrative embodiment of the presentmethods.

FIG. 2 shows the size distribution of resin particles of anothermonodisperse latex formed according to an illustrative embodiment of thepresent methods.

FIG. 3 shows a scanning transmission electron microscope (STEM) image ofa dried monodisperse latex formed according to an illustrativeembodiment of the present methods. This image shows localcrystallization and demonstrates the ability to form three-dimensional(3D) photonic crystals.

DETAILED DESCRIPTION Monodisperse Latex

In one aspect, methods for forming a monodisperse latex are provided.The latex comprises resin particles synthesized from certain monomersaccording to the present methods, which are further described below. Thefollowing monomers and combinations thereof may be used (use of “(meth)”as in, e.g., “(meth)acrylate”, refers to both acrylate andmethacrylate): styrene; alkyl (meth)acrylates, such as, methyl acrylate,ethyl acrylate, butyl acrylate, isobutyl acrylate, dodecyl acrylate,n-octyl acrylate, 2-chloroethyl acrylate, methyl methacrylate, ethylmethacrylate and butyl methacrylate; β-carboxy ethyl acrylate (β-CEA),phenyl acrylate, methyl alphachloroacrylate; butadiene; isoprene;methacrylonitrile; acrylonitrile; vinyl ethers, such as vinyl methylether, vinyl isobutyl ether, and vinyl ethyl ether; vinyl esters, suchas vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate;vinyl ketones, such as vinyl methyl ketone, vinyl hexyl ketone andmethyl isopropenyl ketone; vinylidene halides, such as vinylidenechloride and vinylidene chlorofluoride; N-vinyl indole; N-vinylpyrrolidone; methacrylate; acrylamide; methacrylamide; vinylpyridine;vinylpyrrolidone; vinyl-N-methylpyridinium chloride; vinyl naphthalene;p-chlorostyrene; vinyl chloride; vinyl bromide; vinyl fluoride;ethylene; propylene; butylenes; and isobutylene. In embodiments, themonomers used to form the resin particles of the latex comprise astyrene and an alkyl acrylate.

Acidic monomers may be used to form the resin particles of themonodisperse latex, including (meth)acrylic acid monomers, sulfonic acidmonomers, sulfonate monomers, and combinations thereof. Illustrativeacidic monomers include acrylic acid, methacrylic acid, ethacrylic acid,dimethylacrylic acid, maleic anhydride, maleic acid, styrenesulfonicacid, vinylsulfonate, cyanoacrylic acid, vinylacetic acid, allylaceticacid, ethylidineacetic acid, propylidineacetic acid, crotonoic acid,fumaric acid, itaconic acid, sorbic acid, angelic acid, cinnamic acid,styrylacrylic acid, citraconic acid, glutaconic acid, aconitic acid,phenylacrylic acid, acryloxypropionic acid, aconitic acid, phenylacrylicacid, acryloxypropionic acid, vinylbenzoic acid, N-vinylsuccinamidicacid, mesaconic acid, methacroylalanine, acryloylhydroxyglycine,sulfoethyl methacrylic acid, sulfopropyl acrylic acid, styrene sulfonicacid, sulfoethylacrylic acid, 2-methacryloyloxymethane-1-sulfonic acid,3-methacryoyloxypropane-1-sulfonic acid, 3-(vinyloxy)propane-1 -sulfonicacid, ethylenesulfonic acid, vinyl sulfuric acid, 4-vinylphenyl sulfuricacid, ethylene phosphonic acid, vinyl phosphoric acid, vinyl benzoicacid, 2-acrylamido-2-methyl-1-propanesulfonic acid, and combinationsthereof. These acidic monomers also encompass salts thereof, e.g., saltof a sulfonic acid.

In embodiments, two different acidic monomers are used to form the resinparticles of the monodisperse latex, each having a different pK_(a)value. The pK_(a) values of the two different acidic monomers may differfrom one another by at least 2 units, at least 3 units, at least 4units, or at least 5 units. In embodiments, the two different acidicmonomers are present in a monomer emulsion used to form the resinparticles at a weight ratio in a range of from 0.1 to 10. This includesa range of from 0.5 to 8 and from 1 to 6. In embodiments, the twodifferent types of acidic monomers used to form the resin particlescomprise a methacrylic acid and a sulfonic acid.

Hydrophilic monomers may be used to form the resin particles of themonodisperse latex. The term “hydrophilic monomer” is distinguished fromthe “acidic monomers” described above. That is, although the selectedacidic monomers may also be hydrophilic, these terms refer to different,chemically distinct species of monomers. The hydrophilic monomers aregenerally monofunctional, i.e., comprising a single polymerizable group.Illustrative hydrophilic monomers include hydroxyethyl (meth)acrylate,n-hydroxyethyl (meth)acrylamide, hydroxypropyl (metha)crylate, andhydroxypropyl (meth)acrylamide, ethylene glycol (meth)acrylate,propylene glycol (meth)acrylate, poly(ethylene glycol) (meth)acrylatehaving a molecular weight from 200 g/mol to 2000 g/mol, andpoly(propylene glycol) (meth)acrylate having a molecular weight from 200g/mol to 2000 g/mol, and combinations thereof. In embodiments, thehydrophilic monomers used to form the resin particles comprise apoly(propylene glycol) methacrylate.

Multifunctional monomers may be used to form the resin particles of themonodisperse latex, i.e., those comprising more than one polymerizablegroup (e.g., 2, 3, 4). These are useful as they facilitate crosslinkingwithin the resin particles. Illustrative multifunctional monomersinclude difunctional monomers such as a poly(ethylene glycol)di(meth)acrylate, e.g., poly(ethylene glycol) diacrylate having amolecular weight from 200 g/mol to 2000 g/mol. These difunctionalmonomers may also be considered to be hydrophilic as noted above. Otherhydrophilic difunctional monomers include a diacrylate compound bondedwith an alkyl chain containing an ether bond, such as diethylene glycoldiacrylate, triethylene glycol diacrylate, tetraethylene glycoldiacrylate, polyethylene glycol #400 diacrylate, polyethylene glycol#600 diacrylate, dipropylene glycol diacrylate, and compounds obtainedby substituting acrylate of these compounds with methacrylate; adiacrylate compound bonded with a chain containing an aromatic group andan ether bond, such aspolyoxyethylene(2)-2,2-bis(4-hydroxyphenyl)propane diacrylate,polyoxyethylene(4)-2,2-bis(4-hydroxyphenyl)propane diacrylate, andcompounds obtained by substituting acrylate of these compounds withmethacrylate. Other illustrative difunctional monomers include a dienecompound, such as isoprene and butadiene, an aromatic divinyl compound,such as divinylbenzene and divinylnaphthalene; a diacrylate compoundbonded with an alkyl chain, such as ethylene glycol diacrylate,1,3-butylene glycol diacrylate, 1,4-butanediol diacrylate,1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, 1,10-dodecanedioldiacrylate, neopentyl glycol diacrylate, and compounds obtained bysubstituting acrylate of these compounds with methacrylate.Multifunctional monomers include such as pentaerythritol triacrylate,trimethylolmethane triacrylate, trimethylolpropane triacrylate,tetramethylolmethane tetraacrylate, oligoester acrylate, and compoundsobtained by substituting acrylate of these compounds with methacrylate.

Reactive surfactants may be used to form the resin particles of themonodisperse latex. Suitable reactive surfactants comprise apolymerizable (and thus, reactive) group such that they becomeincorporated into the resin particles. Illustrative reactive surfactantsinclude anionic ether sulfate reactive surfactants such as those in thecommercially available Hitenol BC series such as Hitenol BC10-25. Othersuitable reactive surfactants include polyoxyethylene alkylphenyl etherammonium sulfate, Hitenol BC-10, BC-20, BC-2020, BC-30; polyoxyethylenestyrenated phenyl ether ammonium sulfate including Hitenol AR-10, AR-20,AR10-25, AR-2020; non-ionic polyoxyethylene alkylphenyl ether includingNoigen RN-10, RN-20, RN-30, RN-40, RN-5065; and reactive surfactantavailable from Ethox including E-sperse RX-201, RX-202, RX-203, RS-1596,RS-1616, RS-1617, RS-1618, RS-1684.

A chain transfer agent may be used to form the monodisperse latex. Thechain transfer agent may be a mercaptan or a thiol. Suitable chaintransfer agents include n-dodecylmercaptan (NDM), n-dodecanethiol (DDT),tert-dodecylmercaptan, 1-butanethiol, 2-butanethiol, octanethiol, andcombinations thereof. Halogenated carbons such as carbon tetrabromide,carbon tetrachloride, and combinations thereof may be used as chaintransfer agents.

In forming the monodisperse latex, any of the monomers described abovemay be used in a monomer emulsion comprising a solvent. Water isgenerally used as the solvent, but water-soluble or water-miscibleorganic solvents (e.g., ethanol) may also be included. The type ofmonomers and their relative amounts may be selected to tune theproperties of the resin particles/latex. However, it has been found thatthe following amounts are useful for achieving resin particles havingsmall sizes and narrow size distributions.

Acidic monomers may be used in the monomer emulsion in an amount in arange of from 1.5 weight % to 15 weight %. (Here, weight % refers to the(total weight of acidic monomers)/(total weight of monomers in themonomer emulsion, excluding the reactive surfactants)*100). This rangeincludes from 5 weight % to 10 weight %. As noted above, two differenttypes of acidic monomers having different pK_(a) values may be used inthe weight ratios described above. Hydrophilic monomers may be used inthe monomer emulsion in an amount in a range of from 0 weight % to 5weight %. (Weight % has a meaning analogous to that described for acidicmonomers.) This range includes from 0.1 weight % to 5% weight % and from1 weight % to 5 weight %. Multifunctional monomers, includingdifunctional monomers, may be used in the monomer emulsion in an amountin a range of from 0.01 to 5 weight %, from 0.1 weight % to 5 weight %,or from 0.1 weight % to 1 weight %. (Weight % has a meaning analogous tothat described for acidic monomers.) Other monomers, (e.g., styrenes,alkyl (meth)acrylates) may be present in an amount in a range of from 70weight % to 97 weight %. (Weight % has a meaning analogous to thatdescribed for acidic monomers.) This range includes from 75 weight % to90 weight %.

Together, the amount of acidic monomers, hydrophilic monomers, andmultifunctional monomers (e.g., hydrophilic multifunctional monomers)may be present in the monomer emulsion in a range of from 1.5 weight %to 12 weight %. (Here, weight % refers to the (total weight of acidicmonomers, hydrophilic monomers, and multifunctional monomers)/(totalweight of monomers in the monomer emulsion, excluding the reactivesurfactants)*100.) This range includes from 2 weight % to 12 weight %,and from 5 weight % to 10 weight %.

Reactive surfactants may be used in the monomer emulsion an amount in arange of from 1.5 weight % to 6.5 weight %. (Here, weight % refers tothe (total weight of reactive surfactants)/(total weight of monomers inthe monomer emulsion, including the reactive surfactant monomers)*100.)This range includes from 1.5 weight % to 5 weight %.

The chain transfer agent(s) may be present in the monomer emulsion andmay be used in various suitable amounts, for example, from 0.25 weight %to 2.5 weight %. (Here, weight % refers to the (total weight of chaintransfer agents)/(total weight of monomers in the monomer emulsion,excluding the reactive surfactants)*100.)

In embodiments, the monomer emulsion comprises (or consists of) asolvent (e.g., water), a styrene, an alkyl acrylate (e.g., butylacrylate), an acidic monomer, a multifunctional monomer (e.g., adifunctional monomer), a reactive surfactant, and a chain transferagent. In such embodiments, one type or different types of the variousmonomers may be used. Similarly, one type or different types of thesolvent and/or one type or different types of the chain transfer agentmay be used. In embodiments, the monomer emulsion comprises (or consistsof) a solvent (e.g., water), a styrene, an alkyl acrylate (e.g., butylacrylate), a methacrylic acid, a hydrophilic monomer (e.g., apoly(propylene glycol) methacrylate), a multifunctional monomer (e.g., adifunctional monomer), a reactive surfactant, and a chain transferagent. In embodiments, the monomer emulsion comprises (or consists of) asolvent (e.g., water), a styrene, an alkyl acrylate (e.g., butylacrylate), two different types of acidic monomers (e.g., a methacrylicacid and a sulfonic acid), a difunctional monomer (e.g., a poly(ethyleneglycol) diacrylate), a reactive surfactant, and a chain transfer agent.In any of these embodiments, amounts of the various monomers and chaintransfer agents may be used as described above. The balance may be madeup of the solvent.

At least in embodiments, the monomer emulsion is free of (i.e., does notcomprise) a surfactant. Here, “surfactant” refers to non-reactive,non-polymerizable anionic surfactants such as sodium dodecylsulfate(SDS), sodium dodecylbenzene sulfonate, sodium dodecylnaphthalenesulfate; dialkyl benzenealkyl sulfates; palmitic acid;alkyldiphenyloxide disulfonate; and branched sodium dodecyl benzenesulfonate. “Surfactant” also refers to non-reactive, non-polymerizablecationic surfactants such as alkylbenzyl dimethyl ammonium chloride,dialkyl benzenealkyl ammonium chloride, lauryl trimethyl ammoniumchloride, alkylbenzyl methyl ammonium chloride, alkyl benzyl dimethylammonium bromide, benzalkonium chloride, cetyl pyridinium bromide,trimethyl ammonium bromide, halide salts of quarternizedpolyoxyethylalkylamines, and dodecylbenzyl triethyl ammonium chlorides.“Surfactant” also refers to non-reactive, non-polymerizable nonionicsurfactants such as polyoxyethylene cetyl ether, polyoxyethylene laurylether, polyoxyethylene octyl ether, polyoxyethylene octylphenyl ether,polyoxyethylene oleyl ether, polyoxyethylene sorbitan monolaurate,polyoxyethylene stearyl ether, polyoxyethylene nonylphenyl ether,dialkylphenoxy poly(ethyleneoxy) ethanol, and block copolymer ofpolyethylene oxide and polypropylene oxide. Thus, the monomer emulsionmay be free of (i.e., does not comprise) any of these surfactants.

The present methods for forming the monodisperse latex comprise addingany of the monomer emulsions described above to a reactive surfactantsolution at a feed rate over a period of time. The reactive surfactantsolution comprises a solvent and a reactive surfactant. Any of thesolvents and any of the reactive surfactants described above may beused. One type or different types of solvent and/or reactive surfactantsmay be used. The reactive surfactant in the reactive surfactant solutionmay be the same type or a different type as compared to a reactivesurfactant that may be present in the monomer emulsion. The reactivesurfactant solution may further comprise a buffer. Various buffers maybe used such as sodium bicarbonate, sodium carbonate, and ammoniumhydroxide. The reactive surfactant may be used in an amount in a rangeof from 1 weight % to 10 weight %. (Here, weight % refers to the (totalweight of reactive surfactants)/(total weight of reactive surfactantsolution)*100.) This range includes from 2 weight % to 5 weight %. Thebuffer may be used in an amount in a range of from 0.25 weight % to 2.5weight %. (Weight % has a meaning analogous to that described above.)

An initiator may be included in the reactive surfactant solution.Alternatively, a separate initiator solution comprising the initiatorand any of the solvents described above may be formed and the separateinitiator solution added to the reactive surfactant solution. Theseparate initiator solution may be added prior to the addition of themonomer emulsion. One type or different types of solvent and/orinitiators may be used. Examples of suitable initiators include watersoluble initiators, such as ammonium persulfate (APS), sodium persulfateand potassium persulfate; and organic soluble initiators includingorganic peroxides and azo compounds including Vazo peroxides, such asVAZO 64™, 2-methyl 2-2′-azobis propanenitrile, VAZO 88™, 2-2′-azobisisobutyramide dehydrate; and combinations thereof. Other water-solubleinitiators which may be used include azoamidine compounds, for example2,2′-azobis(2-methyl-N-phenylpropionamidine) dihydrochloride,2,2′-azobis[N-(4-chlorophenyl)-2-methylpropionamidine]di-hydrochloride,2,2′-azobis[N-(4-hydroxyphenyl)-2-methyl-propionamidine]dihydrochloride,2,2′-azobis[N-(4-amino-phenyl)-2-methylpropionamidine]tetrahydrochloride,2,2′-azobis[2-methyl-N-(phenylmethyl)propionamidine]dihydrochloride,2,2′-azobis[2-methyl-N-2-propenylpropionamidine]dihydrochloride,2,2′-azobis[N-(2-hydroxy-ethyl)2-methylpropionamidiene]dihydrochloride,2,2′-azobis[2(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(4,5,6,7-tetrahydro-1H-1,3-diazepin-2-yl)propane]dihydrochloride,2,2′-azobis[2-(3,4,5,6-tetrahydropyrimidin-2-yl)propane]dihydrochlo-ride,2,2′-azobis[2-(5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl)propane]di-hydrochloride, 2,2′-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride, andcombinations thereof. The initiator may be used in an amount in a rangeof from 0.1 weight % to 2.5 weight %. (Here, weight % refers to the(total weight of initiators)/(total weight of reactive surfactantsolution)*100.)

In embodiments, the reactive surfactant solution comprises (or consistsof) a solvent (e.g., water), a reactive surfactant, and optionally, oneor more of an initiator and a buffer. In such embodiments, one type ordifferent types of these components may be used. In any of theseembodiments, amounts of the reactive surfactants, initiator, and buffermay be used as described above. The balance may be made up of thesolvent. At least in some embodiments, the reactive surfactant solutionis free of (i.e., does not comprise) any of the surfactants describedabove. In at least some embodiments, the reactive surfactant solution isfree of (i.e., does not comprise) any monomers, other than the reactivesurfactant monomer(s) present in the solution.

The addition of the monomer emulsion to the reactive surfactant solutionmay be carried out under an inert gas (e.g., nitrogen) and at anelevated temperature (e.g., greater than room temperature such as atemperature in a range of from 50° C. to 90° C.). This may beaccomplished by purging with the inert gas and heating the reactivesurfactant solution prior to the addition of the monomer emulsion andcontinuing during the addition of the monomer emulsion.

As noted above, the monomer emulsion is added at a feed rate over aperiod of time. In the presence of the initiator, the monomers of themonomer emulsion undergo polymerization reactions to form the resinparticles of the monodisperse latex. The feed rate is sufficiently slowso that the polymerization is carried out under “monomer-starved”conditions. This means that the feed rate is no greater than the ratethe polymerization reactions, e.g., between styrene and acrylatemonomers. Illustrative feed rates include those in a range of from 1mL/min to 10 mL/min based on a total reaction volume of 1 L.Illustrative periods of time include those in a range of from 60 minutesto 600 minutes. After the monomer emulsion has been added, thepolymerization may be allowed to continue for an additional period oftime. Illustrative additional periods of time include those in a rangeof from 1 hour to 18 hours. Both the addition of the monomer emulsionand the polymerization after addition may be carried out under the inertgas and at the elevated temperature. Optionally, the latex formed may beprocessed by standard techniques such as coagulation, dissolution andprecipitation, filtering, washing, or drying. If solvent/water isremoved from the latex, e.g., via drying, the dried latex stillcomprises the resin particles, which may be used to form the aqueousinkjet ink composition described below. Thus, any of the disclosedaqueous inkjet ink compositions may simply comprise the resin particlesof any of the disclosed latexes.

It is noted that, at least in embodiments, the present methods do notinvolve the use of a resin seed in forming the resin particles of themonodisperse latex. This is by contrary to existing processes which makeuse of resin seeds in order to initiate and stabilize polymerization.Thus, in such embodiments, neither the monomer emulsion nor the reactivesurfactant solution comprises such a resin seed. The polymerizationreactions that form the resin particles also do not involve such a resinseed. Similarly, at least in embodiments, the present methods do notinvolve the use of any of the surfactants (other than the reactivesurfactant monomers) described above.

The present methods may further comprise forming the monomer emulsion,forming the reactive surfactant solution, and/or forming the initiatorsolution. Each may be formed by combining the desired components at thedesired amounts and mixing.

As noted above, the monodisperse latex formed by the present methodscomprises resin particles having a small size and narrow distribution.The composition of the resin particles depends upon the selection of themonomers and their relative amounts and the polymerization reactionsbetween selected monomers that produce a polymerization product asdescribed above. Thus, a variety of compositions are encompassed basedon the description above, including those based on variouspolymerization products comprising various combinations of monomers.However, in embodiments, the resin particles comprise (or consist of)the polymerization product (e.g., a copolymer) of reactants comprising astyrene, an alkyl acrylate (e.g., butyl acrylate), an acidic monomer, amultifunctional monomer (e.g., a difunctional monomer), and a reactivesurfactant. In such embodiments, one type or different types of thevarious monomers may be present. In embodiments, the resin particlescomprise (or consist of) the polymerization product of reactantscomprising a styrene, an alkyl acrylate (e.g., butyl acrylate), amethacrylic acid, a hydrophilic monomer (e.g., a poly(propylene glycol)methacrylate), a multifunctional monomer (e.g., a difunctional monomer),and a reactive surfactant. In embodiments, the resin particles comprise(or consist of) the polymerization product of reactants comprising astyrene, an alkyl acrylate (e.g., butyl acrylate), two different typesof acidic monomers (e.g., a methacrylic acid and a sulfonic acid), adifunctional monomer (e.g., a poly(ethylene glycol) diacrylate), and areactive surfactant. In each of these embodiments, an initiator may beincorporated at the beginning and end of each polymer chain in the resinparticles. In each of these embodiments, the resin may be crosslinkeddue to the multifunctional/difunctional monomer. In each of theseembodiments, the monomers may be present in the resin particles in theamounts described above.

The resin particles of the present monodisperse latexes may becharacterized by their size. The size may be reported as a D_((z, ave))value, measured using a nanoparticle analyzer such as a MalvernNano-Zetasizer. In embodiments, the D_((z, ave)) is no greater than 150nm, no greater than 120 nm, no greater than 110 nm, no greater than 100nm, or in a range of from 60 nm to 150 nm or from 60 nm to 100 nm.

Similarly, the resin particles of the present monodisperse latexes maybe characterized by their size distribution. The size distribution maybe reported as a polydispersity index (PDI), measured using ananoparticle analyzer such as a Malvern Nano-ZS. In embodiments, the PDIis no greater than 0.1, no greater than 0.050, no greater than 0.025, nogreater than 0.010, no greater than 0.005 or in a range of from 0.001 to0.1.

Due to their small size and narrow size distribution, the resinparticles of the present monodisperse latexes may further becharacterized as being free of (i.e., not comprising) large particles.This may be evidenced by a D_((v, 90))value of less than 200 nm, lessthan 175 nm, or less than 150 nm.

The small size and narrow size distribution of the present monodisperselatexes may be further evidenced by the ability to formthree-dimensional (3D) photonic crystals upon removal of solvent (i.e.,drying) from the latex. Such crystal formation is possible because ofthe uniform size of the resin particles. Local crystallization and theability to form the 3D photonic crystals may be confirmed using scanningtunneling electron microscopy (STEM). (See FIG. 3.) Controlled heatingmay be used to achieve the 3D photonic crystals.

Aqueous Inkjet Ink Compositions

Any of the monodisperse latexes described above may be used to providean aqueous inkjet ink composition. As noted above, it is believed thatthe small size and narrow distribution of the resin particles of thelatexes contribute, at least in part, to greatly improved stability andprinting performance of the aqueous inkjet ink compositions. The latexmay be present in the aqueous inkjet ink composition in an amount in arange of from 1 weight % to 10 weight %. (Here, weight % refers to the(total weight of dry latex)/(total weight of aqueous inkjet inkcomposition)*100.) This range includes from 5 weight % to 10 weight %. Avariety of other components may be used to form the aqueous inkjet inkcompositions as described below.

Solvent System

The aqueous inkjet ink compositions comprise a solvent system based onwater. The solvent system can consist solely of water, or can comprise amixture of water and a water-soluble and/or water-miscible organicsolvent. The water-soluble and water-miscible organic solvents may bereferred to herein as a co-solvent or a humectant. Suitable such organicsolvents include alcohols and alcohol derivatives, including aliphaticalcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers,long chain alcohols, primary aliphatic alcohols, secondary aliphaticalcohols, 1,2-alcohols, 1,3-alcohols, 1,5-alcohols, ethylene glycolalkyl ethers, propylene glycol alkyl ethers, methoxylated glycerol, andethoxylated glycerol. Illustrative examples include ethylene glycol,propylene glycol, diethylene glycols, glycerine, dipropylene glycols,trimethylolpropane, 1,2-hexanediol, 1,5-pentanediol,2-methyl-1,3-propanediol, 2-ethyl-2-hydroxymethyl-1,3-propanediol,3-methoxybutanol, 3-methyl-1,5-pentanediol, 1,3-propanediol,1,4-butanediol, and 2,4-heptanediol. Other suitable solvents includeamides, ethers, urea, substituted ureas such as thiourea, ethylene urea,alkylurea, alkylthiourea, dialkylurea, and dialkylthiourea, carboxylicacids and their salts, such as 2-methylpentanoic acid,2-ethyl-3-propylacrylic acid, 2-ethyl-hexanoic acid, 3-ethoxyproponic,acid, and the like, esters, organosulfides, organosulfoxides, sulfones(such as sulfolane), carbitol, butyl carbitol, cellusolve, ethers,tripropylene glycol monomethyl ether, ether derivatives, hydroxyethers,amino alcohols, ketones, N-methylpyrrolidinone, 2-pyrrolidinone,cyclohexylpyrrolidone, amides, sulfoxides, lactones, polyelectrolytes,methyl sulfonylethanol, imidazole, 1,3-dimethyl-2-imidazolidinone,betaine, sugars, such as 1-deoxy-D-galactitol, mannitol, inositol, andthe like, substituted and unsubstituted formamides, and substituted andunsubstituted acetamides. Combinations of these organic solvents may beused.

Suitable water-soluble and/or water-miscible organic solvents include aglycol of hydrocarbons having a carbon number of 4 to 7. Examples ofsuch a glycol include 1,2-pentane diol; 1,2-hexanediol; 1,5-pentanediol;1,6-hexanediol; 3-methyl-1,3-butanediol; 1,2-butanediol;2,4-pentanediol; 1,7-heptanediol; 3-methyl-1,5-pentanediol;trimethylolpropane; ethyleneurea; 1,2,6-hexantriol; 1,2,3-butanetriol;sorbitol; urea; diethylene glycol; 1,2,4-butanetriol; glycerol;diglycerol; triethylene glycol; polyethylene glycol 200; andpolyethylene glycol 600.

In embodiments, the solvent system comprises water, a 1,2-alcohol (e.g.,1,2-hexanediol), a glycol (e.g., propylene glycol), and a glycerol.

In solvent systems comprising water and an organic solvent, the water toorganic solvent weight ratio, as well as the type and relative amount ofdifferent organic solvents, may be selected to achieve certainproperties for the aqueous inkjet ink composition such as a desiredsurface tension, viscosity, etc. In embodiments, the water to organicsolvent weight ratio is from 90:10 to 51:49. If more than one organicsolvent is used, these weight ratios refer to the total amount oforganic solvent. As water may be present in the latex, colorant, etc.,these weight ratios refer to the total amount of water.

Similarly, various total amounts of the solvent system may be used inthe aqueous inkjet ink compositions. In embodiments, the solvent systemis present in an amount of from 50 weight % to 95 weight %, from 60weight % to 90 weight %, or from 65 weight % to 90 weight %. (Here,weight % refers to the (total weight of solvent system)/(total weight ofaqueous inkjet ink composition)*100.) In embodiments, the total amountof water present is at least 50 weight %, at least 60 weight %, at least80 weight %, or in a range of from 50 weight % to 95 weight %. (Here,weight % refers to the (total weight of water)/(total weight of aqueousinkjet ink composition)*100.)

Water-Soluble Resin

A water-soluble resin may be used in the aqueous inkjet ink composition.The type and the amount may be also selected to achieve a desiredviscosity. Illustrative water-soluble resins include polyethylene glycoland polyvinylpyrrolidone. Molecular weights for the water-soluble resinsmay be in a range of from 1000 g/mol to 10,000 g/mol. However, it hasbeen found that at least some embodiments of the aqueous inkjet inkcompositions are surprisingly sensitive to the type and molecular weightof the water-soluble resin. This finding is further described in theExamples, below. In embodiments, the water-soluble resin is polyethyleneglycol having a molecular weight in a range of from 3000 g/mol to 9000g/mol, from 3000 g/mol to 7000 g/mol, from 3000 g/mol to 5000 g/mol, or4000 g/mol. These molecular weight values may be determined using gelpermeation chromatography. In embodiments, the amount of thewater-soluble resin is selected such that the total solids content(generally provided by the latex, the water-soluble resin, and thecolorant) of the aqueous inkjet ink composition is from 5 weight % to 15weight %, from 6 weight % to 12 weight %, or from 7 weight % to 10weight %. (Here, weight % refers to the (total weight of solids)/(totalweight of aqueous inkjet ink composition)*100.)

The aqueous inkjet ink composition may further comprise other binderresins including acrylic polymers such as styrene-acrylic copolymers andvinylpyrrolidone copolymers, urethane or polyurethane dispersions, andacrylic-urethane hybrid dispersions. More specific binder resins thatcan be used include those available from Johnson Polymers (BASF) such asJoncryl 661, Joncryl 8003, Joncryl 8078, Joncryl 8082, Joncryl 537,Joncryl H538, Joncryl H538, Joncryl including the name of HPD 71E. Otherexemplary water-soluble resins include Rhoplex I-1955, Rhoplex I-2426D,Rhoplex I-62, Rhoplex I-98, Rhoplex E-1691, available from Rhohm & Haas.Others include Lucidene 190, Lucidene 400, and Lucidene 243, availablefrom DSM Corporation; NeoCryl A-1110, NeoCryl A-2092, NeoCryl A-639,NeoRad R-440, NeoRad R-441, NeoRez N-55 under the name 972, PVP K-15,PVP K-30, PVP K-60, PVP K-85, Ganex P-904LC, PVP/VA W-63 available fromISP.

Colorant

The aqueous inkjet ink composition may comprise a colorant. Colorantsinclude pigments, dyes, and combinations thereof. Examples of suitabledyes include anionic dyes, cationic dyes, nonionic dyes, andzwitterionic dyes. Specific examples of suitable dyes include Food dyessuch as Food Black No. 1, Food Black No. 2, Food Red No. 40, Food BlueNo. 1, Food Yellow No. 7, FD & C dyes, Acid Black dyes (No. 1, 7, 9, 24,26, 48, 52, 58, 60, 61, 63, 92, 107, 109, 118, 119, 131, 140, 155, 156,172, 194), Acid Red dyes (No. 1, 8, 32, 35, 37, 52, 57, 92, 115, 119,154, 249, 254, 256), Acid Blue dyes (No. 1, 7, 9, 25, 40, 45, 62, 78,80, 92, 102, 104, 113, 117, 127, 158, 175, 183, 193, 209), Acid Yellowdyes (No. 3, 7, 17, 19, 23, 25, 29, 38, 42, 49, 59, 61, 72, 73, 114,128, 151), Direct Black dyes (No. 4, 14, 17, 22, 27, 38, 51, 112, 117,154, 168), Direct Blue dyes (No. 1, 6, 8, 14, 15, 25, 71, 76, 78, 80,86, 90, 106, 108, 123, 163, 165, 199, 226), Direct Red dyes (No. 1, 2,16, 23, 24, 28, 39, 62, 72, 236), Direct Yellow dyes (No. 4, 11, 12, 27,28, 33, 34, 39, 50, 58, 86, 100, 106, 107, 118, 127, 132, 142, 157),Reactive Dyes, such as Reactive Red Dyes (No. 4, 31, 56, 180), ReactiveBlack dyes (No. 31), Reactive Yellow dyes (No. 37); anthraquinone dyes,monoazo dyes, disazo dyes, phthalocyanine derivatives, including variousphthalocyanine sulfonate salts, aza(18)annulenes, formazan coppercomplexes, and triphenodioxazines.

Examples of suitable pigments include black pigments, cyan pigments,magenta pigments, and yellow pigments. Pigments can be organic orinorganic particles. Suitable inorganic pigments include carbon black.However, other inorganic pigments may be suitable such as cobalt blue(CoO—Al₂O₃), chrome yellow (PbCrO₄), and iron oxide. Suitable organicpigments include, for example, azo pigments including diazo pigments andmonoazo pigments, polycyclic pigments (e.g., phthalocyanine pigmentssuch as phthalocyanine blues and phthalocyanine greens), perylenepigments, perinone pigments, anthraquinone pigments, quinacridonepigments, dioxazine pigments, thioindigo pigments, isoindolinonepigments, pyranthrone pigments, and quinophthalone pigments), insolubledye chelates (e.g., basic dye type chelates and acidic dye typechelate), nitro pigments, nitroso pigments, and anthanthrone pigmentssuch as PR168. Representative examples of phthalocyanine blues andgreens include copper phthalocyanine blue, copper phthalocyanine green,and derivatives thereof (Pigment Blue 15, Pigment Green 7, and PigmentGreen 36). Representative examples of quinacridones include PigmentOrange 48, Pigment Orange 49, Pigment Red 122, Pigment Red 192, PigmentRed 202, Pigment Red 206, Pigment Red 207, Pigment Red 209, PigmentViolet 19, and Pigment Violet 42. Representative examples ofanthraquinones include Pigment Red 43, Pigment Red 194, Pigment Red 177,Pigment Red 216 and Pigment Red 226. Representative examples ofperylenes include Pigment Red 123, Pigment Red 149, Pigment Red 179,Pigment Red 190, Pigment Red 189 and Pigment Red 224. Representativeexamples of thioindigoids include Pigment Red 86, Pigment Red 87,Pigment Red 88, Pigment Red 181, Pigment Red 198, Pigment Violet 36, andPigment Violet 38. Representative examples of heterocyclic yellowsinclude Pigment Yellow 1, Pigment Yellow 3, Pigment Yellow 12, PigmentYellow 13, Pigment Yellow 14, Pigment Yellow 17, Pigment Yellow 65,Pigment Yellow 73, Pigment Yellow 74, Pigment Yellow 90, Pigment Yellow110, Pigment Yellow 117, Pigment Yellow 120, Pigment Yellow 128, PigmentYellow 138, Pigment Yellow 150, Pigment Yellow 151, Pigment Yellow 155,and Pigment Yellow 213. Such pigments are commercially available ineither powder or press cake form from a number of sources including,BASF Corporation, Engelhard Corporation, and Sun Chemical Corporation.Examples of black pigments that may be used include carbon pigments. Thecarbon pigment can be almost any commercially available carbon pigmentthat provides acceptable optical density and print characteristics.Carbon pigments suitable for use in the present system and methodinclude, without limitation, carbon black, graphite, vitreous carbon,charcoal, and combinations thereof. Such carbon pigments can bemanufactured by a variety of known methods, such as a channel method, acontact method, a furnace method, an acetylene method, or a thermalmethod, and are commercially available from such vendors as CabotCorporation, Columbian Chemicals Company, Evonik, and E.I. DuPont deNemours and Company. Suitable carbon black pigments include, withoutlimitation, Cabot pigments such as MONARCH® 1400, MONARCH® 1300,MONARCH® 1100, MONARCH® 1000, MONARCH® 900, MONARCH® 880, MONARCH® 800,MONARCH® 700, CAB-O-JET® 200, CAB-O-JET® 300, CAB-O-JET® 450, REGAL®,BLACK PEARLS®, ELFTEX®, MOGUL®, and VULCAN® pigments; Columbian pigmentssuch as RAVEN® 5000, and RAVEN® 3500; Evonik pigments such as ColorBlack FW 200, FW 2, FW 2V, FW 1, FW18, FW 5160, FW 5170, Special Black6, Special Black 5, Special Black 4A, Special Black 4, PRINTEX® U,PRINTEX® 140U, PRINTEX® V, and PRINTEX® 140V. Other pigments includeCAB-O-JET 352K, CAB-O-JET 250C, CAB-O-JET 260M, CAB-O-JET 270Y,CAB-O-JET 465M, CAB-O-JET 470Y and CAB-O-JET 480V (available from CabotCorporation).

The above list of pigments includes unmodified pigment particulates,small molecule attached pigment particulates, and polymer-dispersedpigment particulates.

In forming the aqueous inkjet ink compositions, the colorant(s) may beprovided as a colorant dispersion comprising the colorant and a solvent(e.g., water). The colorant may be in the form of a particle and have anaverage particle size of from 20 nm to 500 nm, from 20 nm to 400 nm, orfrom 30 nm to 300 nm.

Various amounts of colorant may be used in the aqueous inkjet inkcompositions. Generally, however, an amount is selected such that thetotal solids content (generally provided by the latex, the water-solubleresin, and the colorant) of the aqueous inkjet ink composition is from 5weight % to 15 weight %, from 6 weight % to 12 weight %, or from 7weight % to 10 weight %. (Here, weight % refers to the (total weight ofsolids)/(total weight of aqueous inkjet ink composition)*100.)

Surfactant

Unlike the monodisperse latex described above, the aqueous inkjet inkcompositions may comprise one or more surfactants. Examples of suitablesurfactants include anionic surfactants (such as sodium lauryl sulfate(SLS), Dextrol OC-40, Strodex PK 90, ammonium lauryl sulfate, potassiumlauryl sulfate, sodium myreth sulfate and sodium dioctyl sulfosuccinateseries), nonionic surfactants (Surfynol® 104 series, Surfynol® 400series, Dynol™ 604, Dynol™ 607, Dynol™ 810, EnviroGem® 360, secondaryalcohol ethoxylate series such as Tergitol™ 15-s-7, Tergitol™ 15-s-9,TMN-6, TMN-100x and Tergitol™ NP-9, Triton™ X-100, etc.) and cationicsurfactants (Chemguard S-106A, Chemguard S-208M, Chemguard S-216M). Somefluorinated or silicone surfactants can be used such as PolyFox™TMPF-136A, 156A, 151N, Chemguard S-'761p, S-'764p, Silsurf® A008,Siltec® C-408, BYK 345, 346, 347, 348 and 349, polyether siloxanecopolymer TEGO® Wet-260, 270 500, etc. Some amphoteric fluorinatedsurfactants can also be used such as alkyl betaine fluorosurfactant oralkyl amine oxide fluorosurfactant such as Chemguard S-500 and ChemguardS-111.

Various amounts of surfactant may be used in the aqueous inkjet inkcompositions. In embodiments, the surfactant is present in an amount ina range of from 0.01 weight % to 2 weight %. (Here, weight % refers tothe (total weight of surfactant)/(total weight of aqueous inkjet inkcomposition)*100.) If more than one type of surfactant is used, theseamounts refer to the total amount of surfactant.

Additives

Various additives may be used in the aqueous inkjet ink compositions totune the properties thereof. Suitable additives include one or more ofbiocides; fungicides; stabilizers; pH controlling agents such as acidsor bases, phosphate salts, carboxylates salts, sulfite salts, aminesalts, buffer solutions; sequestering agents such as EDTA(ethylenediamine tetra acetic acid); defoamers; and wetting agents.

Various amounts of the additives may be used in the aqueous inkjet inkcompositions. In embodiments, the additives are present in an amount ina range of from 0.01 weight % to 5 weight %. (Here, weight % refers tothe (total weight of additives)/(total weight of aqueous inkjet inkcomposition)*100.) If more than one type of additive is used, theseamounts refer to the total amount of additives.

In at least embodiments, the present aqueous inkjet ink compositions arefree of (i.e., do not comprise) a coagulant and are free of (i.e., donot comprise) a coalescing agent and are free of (i.e., do not comprise)a plasticizer. In embodiments, the ink compositions are free of (i.e.,do not comprise) any pyrrolidone-based solvents such asN-methylpyrrolidone, and are free of (i.e., do not comprise) Texanol andTexanol isobutyrate.

Similarly, the present aqueous inkjet ink compositions may be free of(i.e., do not comprise) a resin other than those provided by the presentmonodisperse latexes. A single type of monodisperse latex may be used.

In embodiments, the aqueous inkjet ink composition comprises (orconsists of) a solvent system; a monodisperse latex; a colorant; andoptionally, one or more of a water-soluble resin and an additive. Inembodiments, the aqueous inkjet ink composition comprises (or consistsof) a solvent system; a monodisperse latex; a colorant; a water-solubleresin; and optionally, an additive. In any of these embodiments, theadditives may be selected from a stabilizer, a surfactant, a defoamer, awetting agent, and a biocide. In any of these embodiments, thecomponents may be selected from any of the solvent systems, monodisperselatexes, colorants, water-soluble resins, and additives disclosedherein. In any of these embodiments, amounts of the components may beused as described above. In any of these embodiments, a single type ofmonodisperse latex may be used. In any of the embodiments in thisparagraph, the phrase “monodisperse latex” may be replaced with “resinparticles.”

The aqueous inkjet ink compositions may be formed by combining thedesired components at the desired amounts and mixing. An illustrativemethod comprises adding any of the disclosed monodisperse latexes (orthe resin particles) to a colorant dispersion to form a first mixture;and adding a second mixture comprising a solvent system and anadditive(s) to the first mixture to form the aqueous inkjet inkcomposition. Mixing and/or heating may be used during the method. Theaqueous inkjet ink composition may be filtered prior to use.Illustrative details are provided in the Examples, below.

The aqueous inkjet ink compositions may be used to form printed images.In embodiments, such a method comprises ejecting droplets of any of thedisclosed aqueous inkjet ink compositions onto a substrate to form animage thereon. Such a method may further comprise incorporating the inkcomposition into an inkjet printing apparatus. The printing apparatusmay employ a thermal inkjet process wherein the ink composition in thenozzles is selectively heated in an imagewise pattern, thereby causingdroplets of the ink composition to be ejected in imagewise pattern.Alternatively, the printing apparatus may employ an acoustic inkjetprocess wherein droplets of the ink composition are caused to be ejectedin imagewise pattern by acoustic beams. In yet another embodiment, theprinting apparatus may employ a piezoelectric inkjet process, whereindroplets of the ink composition are caused to be ejected in imagewisepattern by oscillations of piezoelectric vibrating elements. Anysuitable substrate can be employed.

The method may comprise ejecting ink droplets in an imagewise patternonto an intermediate transfer member, heating the image to partially orcompletely remove solvents, and transferring the ink composition in theimagewise pattern from the intermediate transfer member to a finalrecording substrate. The intermediate transfer member may be heated to atemperature above that of the final recording sheet and below that ofthe ink composition in the printing apparatus. An offset or indirectprinting process is also disclosed in, for example, U.S. Pat. No.5,389,958, the disclosure of which is totally incorporated herein byreference.

Any suitable substrate or recording sheet can be employed as the finalrecording sheet. Illustrative substrates include McCoy® Gloss #100coated substrate, Xerox® Bold uncoated substrate, Kodak photo paper,Sterling® Ultra Web Matte (offset coated), TrueJet® Gloss Text (Inkjettreated coated), and McCoy® Silk (offset coated).

EXAMPLES

The following Examples are being submitted to further define variousspecies of the present disclosure. These Examples are intended to beillustrative only and are not intended to limit the scope of the presentdisclosure. Also, parts and percentages are by weight unless otherwiseindicated. As used herein, “room temperature” refers to a temperature offrom about 20° C. to about 25° C.

Example 1

A reactive surfactant solution of 1.6 grams (Hitenol BC1025 fromMontello), 36 grams deionized water and 0.4 g NaHCO₃ was prepared bymixing in a glass reactor. The reaction was then purged with nitrogenfor 30 minutes. The reactor was then continuously purged with nitrogenwhile being stirred at 250 rpm. The reactor was then heated up to 85° C.and held there. Separately, 0.2 grams of ammonium persulfate initiatorwas dissolved in 5 grams of deionized water and added to the reactor.

Separately, a monomer emulsion was prepared in the following manner: 30g of styrene, 5 g of butyl acrylate, 3 g of methacrylic acid, 1.5 g ofpolypropylene glycol methacrylate 370, 0.6 g of 1-dodecanethiol (DDT),0.12 g of PEGDA 250, 0.8 g of Hitenol BC 1025, and 15 g of deionizedwater were mixed with intermittent mixing to form an emulsion. Theemulsified mixture was fed to the reactor slowly for 3 h and thereaction continued for 15 h. The resulting latex was passed through a 25μm filter and neutralized to pH 8.0 with 0.5 M KOH solution.

A Malvern Nano-ZS was used to analyze the dimensions of the resinparticles. The distribution of sizes of the resin particles of theresulting latex are shown in FIG. 1. The peak at 101.0 nm has a width of25.16 nm and includes 100% by volume of the resin particles. Otherparameters were as follows: D_((v, 10)=)71 nm, D_((v, 50))=97 nm, andD_((v, 90))=138 nm; D_((z, ave))=110 nm, and PDI=0.004.

STEM images of the dried latex showed local crystallization,demonstrating the ability to form three-dimensional (3D) photoniccrystals.

Example 2

A reactive surfactant solution of 1.6 grams (Hitenol BC1025 fromMontello), 36 grams deionized water, and 0.4 g NaHCO₃ was prepared bymixing in a glass reactor. The reaction was then purged with nitrogenfor 30 minutes. The reactor was then continuously purged with nitrogenwhile being stirred at 250 rpm. The reactor was then heated up to 85° C.and held there. Separately, 0.2 grams of ammonium persulfate initiatorwas dissolved in 5 grams of deionized water and added to the reactor.

Separately, a monomer emulsion was prepared in the following manner: 31g of styrene, 5 g of butyl acrylate, 3 g of methacrylic acid, 0.5 g ofstyrenesulfonic acid, 0.6 g of 1-dodecanethiol (DDT), 0.12 g of PEGDA250, 0.6 g of Hitenol BC 1025, and 15 g of deionized water were mixedwith intermittent mixing to form an emulsion. The emulsified mixture wasfed to the reactor slowly for 3 h and the reaction continued for 15 h.The resulting latex was passed through a 25 μm filter and neutralized topH 8.0 with 0.5 M KOH solution.

A Malvern Nano-ZS was used to analyze the dimensions of the resinparticles. The distribution of sizes of the resin particles of theresulting latex are shown in FIG. 2. The peak at 86.74 nm has a width of22.49 nm and includes 100% by volume of the resin particles. Otherparameters were as follows: D_((v, 10))=61 nm, D_((v, 50))=83 nm, andD_((v,90))=119 nm, D_((z, ave))=95 nm, and PDI=b 0.023.

As shown in FIG. 3, STEM images of the dried latex show localcrystallization and demonstrates the ability to form three-dimensional(3D) photonic crystals.

Example 3

An aqueous inkjet ink composition was formed using the latex of Example2. The following steps were used to form the aqueous inkjet inkcomposition shown in Table 1, below:

1. The pigment dispersion was added to deionized water and mixed forabout 15 minutes at a speed of about 950 RPM, using a pitched bladepropeller.

2. The latex of Example 2 was added slowly to the pigment dispersion andmixed for about 45 minutes (Mixture A).

3. In a separate beaker, the water-soluble resin, the co-solvents,humectant, stabilizer, surfactant, and wetting agent were mixed to forma homogenous mixture (Mixture B).

4. Mixture B was slowly added into Mixture A. Once the addition wascomplete, the mixer speed was set to about 650 RPM and the componentswere allowed to mix for another ˜75 minutes.

5. The defoamer was added and mixing continued for about another 15minutes.

6. After mixing, the ink composition was left at room temperature forabout 60 minutes before checking pH, conductivity and surface tension.

7. The ink composition was left overnight and then filtered (KST-47filtration apparatus available from Advantec MFS, Inc.) through a glassfiber filter (0.45 μm or 1 μm).

TABLE 1 Aqueous Inkjet Ink Composition Component Chemical Amount SolventWater 8.95 Colorant CAB-O-JET ® 450 28 (15% solids) Latex Latex ofExample 2 7.7 Water-Soluble Resin PEG 4000 (15% solids) 16.65 Co-solvent1 1,2-hexanediol 7 Co-solvent 2 Propylene glycol 28.5 Humectant Glycerol2 Stabilizer Triethanolamine 0.4 Defoamer BYK024 0.2 Surfactant Silicone(Byk 349) 0.5 Wetting Agent Multifunctional nonionic 0.1 surfactantSurfynol 104H (75% active) Total % 100

Stability

The particle size and PDI of the particles of the ink composition weremeasured before and after air oven aging at 60° C. for 3 days using aMalvern Nano-Zetasizer. The results are shown in Table 2. The minimalchange in D_((z, ave)) (˜4%) and no change in PDI demonstrates that theink composition was extremely stable. In addition, the change inviscosity of the ink was negligible (less than 2%) after air oven agingat 60° C. for 3 days.

TABLE 2 Stability of Aqueous Inkjet Ink Composition. ConditionD_((z, ave)) (nm) PDI D_((v,10)) (nm) D_((v, 50)) (nm) D_((v, 90)) (nm)Before 88 0.25 54 87 165 After air 84 0.25 46 76 158 oven aging at 60°C. for 3 days

Printing Performance

The ink composition was jetted using a Dimatix DMP2800 printer ondifferent paper substrates, including Kodak photo paper, McCoy® gloss#100 and Xerox® Bold. The test key parameters used were as follows: Dropmass=4.5-4.8 ng, Drop velocity=7m/s, frequence=5 kHz, Voltage=16-20 V,printing temperature was 20° C. to 40° C. The print parameter was a600×600 dpi print. The measurement was done using a PIAS II instrument,which is a personal image analysis system with a digital loupe. Thehigh-resolution optic module ˜5μm/ pixel was used which has a field viewof ˜3.2 mm×2.4 mm to measure the dot size and diameter. The results areshown in Table 3. In addition, the ink composition passed continuousjetting for >25 minutes demonstrating excellent latency.

TABLE 3 Printing Performance of Aqueous Inkjet Ink Composition. Dotdiameter Line width Optical Substrate (μm) (mm) Circularity DensityMcCoy gloss 51.7 0.044 1.0 ~1.0 #100 Xerox Bold 55.4 0.055 1.0 ~1.0

Shelf-Life

After the jetting of the ink composition, the ink composition was keptin the same printing cartridge for eight days at room temperature. Aftereight days, the ink composition was jetted again. All the nozzlesstarted jetting without any sign of blockage. All nozzles jettedcontinuously for >15 minutes before the test was stopped. Thisexperiment further demonstrates the extended shelf-life and colloidalstability of the ink composition.

Example 4

A series of experiments were conducted to investigate the effect of thewater-soluble resin in a latex-free version of the aqueous inkjet inkcomposition. Table 4, below, lists the samples prepared. Table 5, below,lists the printing parameters tested and the results.

TABLE 4 Latex-free Aqueous Inkjet Ink Compositions. Amount in 100 gComponent Chemical formulation Control A B C D E F Solvent Water 33.6210.09 1.41 4.09 5.29 5.97 1.66 2.01 Colorant CAB-O-JET ® 450 28 19.9119.91 19.91 19.91 19.91 19.91 19.91 (15% solids) Latex Latex of Example2 0 Co-solvent 1 1,2-hexanediol 6.3 Co-solvent 2 Propylene glycol 28.3Humectant Glycerol 2 Stabilizer Triethanolamine 0.9 Surfactant Byk 3490.5 Wetting Agent Surfynol 104H 0.38 (75% active) Water-Soluble PEG 14508.68 Resin (15% solids) PEG 4000 (15% solids) 6 PEG 6000 (15% solids)4.8 PEG 8000 (15% solids) 4.12 PVP 3500 (15% solids) 8.43 PVP 8000 (15%solids) 8.08 Total (g) 100 30.0 30.0 30.0 30.0 30.0 30.0 30.0 ViscosityZero- 6.1 8.43 8.76 8.6 8.99 7.98 8.41 shear (cP) at 23.3° C.

TABLE 5 Printing Performance of Latex-free Aqueous Inkjet InkCompositions. Printing Parameter Control A B C D E F Print Head 32 37 3737 37 37 37 Temperature (° C.) Drop Mass (ng) 4.5 4.8 4.8 4.9 4.9 4.84.9 Drop Velocity (m/s) 6 7 7 6 6 6 6 Voltage (V) 15 17 17 18 17 17 17Jetting Comments Very good Poor Good Acceptable Acceptable Poor GoodFront Face Very clean Significant No Some Some Significant Somesputtering sputtering sputtering sputtering Sputtering sputteringLatency Very good Poor Good Poor Poor Poor Very good

The results show that although all the water-soluble resins achieveacceptable viscosity, the printing performance is highly sensitive tothe type and molecular weight of the water-soluble resin used. The bestperformance is achieved with PEG 4000.

The word “illustrative” is used herein to mean serving as an example,instance, or illustration. Any aspect or design described herein as“illustrative” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Further, for the purposes ofthis disclosure and unless otherwise specified, “a” or “an” means “oneor more.”

All numeric values of parameters in the present disclosure are proceededby the term “about” which means approximately. This encompasses thosevariations inherent to the measurement of the relevant parameter asunderstood by those of ordinary skill in the art. This also encompassesthe exact value of the disclosed numeric value and values that round tothe disclosed numeric value.

The foregoing description of illustrative embodiments of the disclosurehas been presented for purposes of illustration and of description. Itis not intended to be exhaustive or to limit the disclosure to theprecise form disclosed, and modifications and variations are possible inlight of the above teachings or may be acquired from practice of thedisclosure. The embodiments were chosen and described in order toexplain the principles of the disclosure and as practical applicationsof the disclosure to enable one skilled in the art to utilize thedisclosure in various embodiments and with various modifications assuited to the particular use contemplated. It is intended that the scopeof the disclosure be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. A method for forming a latex, the methodcomprising: adding a monomer emulsion comprising water, a monomer, anacidic monomer, a multifunctional monomer, a first reactive surfactant,and a chain transfer agent, to a reactive surfactant solution comprisingwater, a second reactive surfactant, and an initiator, at a feed rateover a period of time so that monomers of the monomer emulsion undergopolymerization reactions to form resin particles in a latex, wherein thereactive surfactant solution does not comprise monomers other than thesecond reactive surfactant, the reactive surfactant solution does notcomprise a resin seed, and the monomer emulsion does not comprise theresin seed.
 2. The method of claim 1, wherein the feed rate is selectedso that the polymerization reactions occur under monomer-starvedconditions.
 3. The method of claim 1, wherein the monomer emulsioncomprises two different acidic monomers having pK_(a) values that differfrom one another by at least about 2 units.
 4. The method of claim 3,wherein the two different acidic monomers are present at a weight ratioof acidic monomer having a higher pK_(a) to acidic monomer having alower pK_(a) in a range of from about 0.1 to about
 10. 5. The method ofclaim 1, wherein the two different acidic monomers are methacrylic acidand a sulfonic acid monomer.
 6. The method of claim 5, wherein thesulfonic acid monomer is styrenesulfonic acid.
 7. The method of claim 1,wherein the monomer emulsion does not comprise a surfactant and thereactive surfactant solution does not comprise a surfactant.
 8. Themethod of claim 1, wherein the monomer emulsion comprises styrene, analkyl acrylate, methacrylic acid, a sulfonic acid monomer, apoly(ethylene glycol) diacrylate, an anionic ether sulfate reactivesurfactant, and the chain transfer agent.
 9. The method of claim 8,wherein the sulfonic acid monomer is styrenesulfonic acid.
 10. Themethod of claim 1, wherein the monomer emulsion comprises styrene, analkyl acrylate, methacrylic acid, a poly(propylene glycol) methacrylate,a poly(ethylene glycol) diacrylate, an anionic ether sulfate reactivesurfactant, and the chain transfer agent.
 11. The method of claim 1,further comprising forming the monomer emulsion and the reactivesurfactant solution.
 12. The method of claim 11, further comprisingforming an initiator solution comprising the initiator and adding theinitiator solution to the reactive surfactant solution prior to addingthe monomer emulsion.
 13. The method of claim 1, wherein the resinparticles have a D_((z, ave)) of no greater than about 150 nm, aD_((v, 90)) of less than about 200 nm, and a polydispersity index (PDI)of no greater than about 0.050.
 14. The method of claim 13, wherein theresin particles have a D_((z, ave)) of no greater than about 120 nm, aD_((v, 90)) of less than about 150 nm, and a PDI of no greater thanabout 0.025.
 15. The method of claim 1, wherein the resin particlescrystallize to form a 3D-photonic crystal upon drying the latex.
 16. Alatex comprising resin particles comprising a polymerization product ofreactants comprising a monomer, an acidic monomer, a multifunctionalmonomer, and a reactive surfactant, the resin particles having aD_((z, ave)) of no greater than about 150 nm, a D_((v, 90)) of less thanabout 200 nm, and a PDI of no greater than about 0.050.
 17. The latex ofclaim 16, wherein the reactants comprise the monomer, two differentacidic monomers having pK_(a) values that differ from one another by atleast about 2 units, the multifunctional monomer, and the reactivesurfactant.
 18. The latex of claim 17, wherein the two different acidicmonomers are present at a weight ratio of acidic monomer having a higherpK_(a) to acidic monomer having a lower pK_(a) in a range of from about0.1 to about
 10. 19. The latex of claim 17, wherein the two differentacidic monomers are methacrylic acid and a sulfonic acid monomer. 20.The latex of claim 19, wherein the sulfonic acid monomer isstyrenesulfonic acid.